The general thrust of our long range plans is to pursue crystallographically structural aspects of molecules of blood coagulation and fibrinolysis with the aim of relating them to functionality at the molecular level. Our research program is presently exclusively devoted to the area. We have already made significant progress by determining the structures of all but one of the important autonomous domains of these molecules. Since blood proteins are generally multi-domain structures, we will now address the problem of domain-domain interactions. In addition, since they interact with other macromolecular substrates, inhibitors, cofactors,..., we will reveal the manner of some of these interactions through the structure determinations of molecular complexes. The specific domain-domain interactions to be investigated are: (l) kringle-kringle (plasminogen (PG) kringles 4-5, PG kringles 1-2-3), (2) kringle-catalytic domain (prethrombin1, prothrombin (PT) kringle2-prethrombin2), (3) epidermal growth factor-like (EGF)-kringle interactions (EGF-urokinase kringle), (4) EGF-EGF and EGF-catalytic domain (thrombomodulin (TM) EGF 4- 5-6-thrombin, TM (408-426) loop-thrombin). Macromolecular interactions with carbohydrates will be determined through low molecular weight heparin complexes with thrombin and the kringle of urokinase and the newly discovered nanomolar single stranded DNA-thrombin interaction will be revealed by the structure of a 15 mer DNA-thrombin complex. We will also complete our studies of metal ion binding to the Gla (gamma- carboxyglutamic acid) phospholipid binding domain of blood molecules with the structure determinations of PT Mg- and Tb-fragment1. These two molecules display deceptively similar properties to Ca-fragment1. However, our work of the past period suggests that the three most likely have very different three-dimensional structures. Diffraction quality single crystals of many of the above have been grown already and their X-ray diffraction patterns examined in a preliminary way.